Running Your First Program

When you write a Python instruction, you are not writing instructions for only one specific operating system. You are writing instructions that the Python interpreter can read and execute. In this course, you will write code in your browser, run it in the course environment, and observe the result. The important distinction is that writing code creates an instruction, while running code causes the interpreter to execute that instruction.

Portability is Python's ability to run on many different operating systems without code changes. Python can support this breadth because it is open-source: its source code is publicly available and can be modified. As a result, Python has been adapted and installed on dozens of platforms, including GNU/Linux, Windows, FreeBSD, and Macintosh, as well as specialized hardware.

The Python interpreter acts as an abstraction layer between your Python code and the underlying operating system. It reads your code and translates it into platform-specific instructions for systems such as Windows, macOS, and Linux. This is why the same Python source can often run on different computers without being rewritten.

Portability is not automatic. It is influenced by the choices you make while writing code. Basic data types, control flow statements, and cross-platform libraries are examples of portable features. By contrast, hard-coded file paths, operating-system-specific system calls, and libraries that have not been ported to all platforms can make a program dependent on one system.

Kivy demonstrates how Python portability can be extended into game development. It allows you to write a single game in Python and deploy it to computers, iPhones, iPads, and Android devices without rewriting the code for each platform.

Kivy provides a portable layer on top of Python. You write code that Kivy understands instead of writing separate code specifically for iOS or Android. Kivy then handles the translation to each platform's native capabilities, allowing one game codebase to reach multiple device types.

This course runs Python code in your browser using a cloud-based interpreter, so you do not need to install Python or configure a local environment. When you write a line of code and press Run, the code is sent to a server. The Python interpreter on that server reads and executes it, and the result is sent back to your browser.

The word print is the function name. The parentheses show that you are calling the function, and the text inside the parentheses is the input, called an argument. When the interpreter reads this statement, it executes print with Hello, Python as its input, so that text appears as output.

Variables are names that hold values. Assignment uses the equals sign to associate a value with a variable name. When Python later encounters the variable name, it looks up the associated value and can use it in another statement.